For basic low cost pumping operations in scientific and industrial markets at rates of up to about 600 m3/hr, the rotary vane pump is still the most commonly used form of vacuum pump. Rotary vane pumps run relatively slowly due to the forces acting on the vanes, which are spring-biased into engagement with a cylindrical wall of the rotor chamber. Rotary screw vacuum pumps may run at higher speeds.
A rotary screw vacuum pump may comprise a housing containing two intersecting bores in which are housed a pair of intermeshing screw rotors. The ends of the housing are closed and provided with suction (inlet) and exhaust (outlet) ports. Working chambers are formed between the walls of the bores and meshing surfaces of the screw rotors. When the screw rotors rotate, the working chambers travel axially along the housing and are progressively limited as they approach the exhaust port end of the housing so that a pulsing pumping action is obtained. Such rotary screw vacuum pumps may be provided with an oil supply system to deliver oil to the screw rotors for lubrication and sealing purposes. Known oil sealed rotary screw vacuum pumps use a Lysholm type screw design that has multiple starts. Typically the screw rotors have at least four starts. The combination of high rotational speeds of the screw rotors and multi-start threads produces a rapidly pulsating output at the exhaust port.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.